1. Field of the Invention
The present invention relates to an ophthalmic apparatus, and more particularly to an ophthalmic apparatus for measuring dryness of a cornea or a conjunctiva of an eye to be examined.
2. Description of Related Art
Right after blinking, a cornea of an eye is covered with a tear film of almost even thickness. This tear film, however, gradually breaks up (drys out), as the eye remains open. It is important to measure the time taken for the breakup (hereinafter, referred to as BUT (Breakup Time)) in order to detect a defect in the tear film. Besides an aqueous layer, the tear film consists of an oil layer on the outermost surface and a mucin layer on the side of the cornea. The aqueous layer is sandwiched between the two layers. The oil layer has a function of protecting moisture from evaporating and the mucin layer has a function of moisten the corneal surface uniformly. To examine a dry eye caused by reduction of moisture (tear deficiency such as Sjogren's syndrome) or by reduction of the mucin layer (Stevens-Johnson syndrome and the like), the BUT measurement is considered to be extremely important.
Conventionally, diagnosis of such a dry eye has been carried out as follows: first fluorescein, which is a fluorescent material, is applied to an eye to be examined, and then the eye is visually observed under a slit lump until it reaches predetermined dryness thereby measuring the BUT mentioned above.
However, in the BUT measurement as described above, dryness of a corneal surface is measured through observing development of dry spots on the corneal surface by an examiner based on his subjective judgement. Naturally, a different examiner leads to a different measurement result and the accuracy of the measurement depends on the examiner's experience. In addition there are other problems. One example is that it is extremely difficult to judge the dryness in the case where dry spots appear non uniformly.